1. Field of the Invention
The present invention relates to a gas turbine generator used in gas turbine cogeneration in which power or electric power and steam are generated to realize energy-saving.
2. Description of the Related Art
According to the configuration of a conventional dual fluid cycle gas turbine generator, for example as shown in FIG. 1, air A sucked in from the atmosphere is compressed by a compressor 1 and fed to a combustor 2. The compressed air becomes a high-temperature combustion gas by the combustion of a fuel F, and led to a turbine 3. After driving the turbine, the combustion gas E generates steam in waste-heat boiler 4 and is emitted into the atmosphere. Steam S generated in waste-heat boiler 4 is injected to the combustor 2, increases the flow of the combustion gas which enters the turbine 3, increases the specific heat of the combustion gas, and increases the output of the turbine 3. The output from the turbine 3 drives the compressor 1 and simultaneously generates electric power by driving a generator 5. An economizer 6 and a stack 9 are provided downstream of the waste-heat boiler 4 which is heated by the waste-heat from the turbine.
On the other hand, according to a conventional regenerative cycle gas turbine generator, for example as shown in FIG. 2, a heat exchanger 7 is provided downstream of the turbine 3. The air A compressed by the compressor 1 is preheated by the turbine waste heat E by the heat exchanger 7, and is fed to the combustor 2 to raise the temperature of the compressed air and to reduce the consumption of fuel F in the combustor 2.
However, in the above-described dual fluid cycle gas turbine generator (FIG. 1), when the entire amount of the steam generated by the waste-heat boiler 4 is injected to the combustor 2, the amount of injected steam reaches 20% to 30% of the taken in air. (1) Consequently, if the injection of steam stops, the flow rate in the turbine is too low and the efficiency of the turbine is badly reduced, thereby considerably lowering the thermal efficiency. (2) Furthermore, since the injected steam is emitted together with the exhaust gas into the atmosphere, there has been a problem that the more the steam is injected, the more the costs for generating the steam from pure water.
On the other hand, in the regenerative cycle gas turbine generator (FIG. 2) described above, since the temperature at the exit of the compressor 1 is high, there has been a problem that the preheating of air is limited and the thermal efficiency cannot be largely improved. With this regenerative cycle gas turbine generator, all of the compressed air from the compressor is preheated by the waste heat in the heat exchanger before it is fed to the combustor. (3) Therefore, the pressure loss in the piping before and after the heat exchanger reduces the thermal efficiency. (4) Additionally, a large thermal capacity causes a problem with control response. (5) Furthermore, a considerably large bypass valve 8 (see FIG. 2) is required to bypass the heat exchanger to prevent the turbine from running at an overspeed during the load shed.
To solve the problem described above, the applicant of the present invention has developed and filed a partial-regenerative dual fluid cycle gas turbine generator (Japanese Patent Application Laid-Open No. 7-248974 in 1995). As shown in FIG. 3, the gas turbine generator includes a gas turbine having a compressor 1, a combustor 2, and a turbine 3; a mixer 10 for compressing air using steam as driving power and mixing both fluids; a superheater 12 for heating a mixed gas with the waste heat of the turbine; a waste-heat boiler 4 for evaporating water using the exhaust of the turbine as a heat source; an air line 15 for feeding a part of the air compressed by the compressor to a combustor and feeding the remainder to the mixer; a main steam line 16 for supplying a part of the steam generated by the waste-heat boiler to the mixer; and a mixed gas line 17 for feeding the mixed gas from the mixer to the combustor through the superheater 12. According to the invention, the amount of the steam injected into the combustor can be reduced, and the pressure loss in the piping before and after the superheater can also be reduced, thereby preventing the thermal efficiency from being lowered.
Recently, for example, a refuse-powered generator system, etc has been suggested using residual steam generated from a refuse incinerator by applying the dual fluid cycle, the regenerative cycle, and the partial regenerative dual fluid cycle shown in FIGS. 1 through 3. According to this refuse generator system, as shown in FIG. 4, residual steam S is heated by the waste heat from the turbine 3, and is provided for the combustor 2 of the gas turbine so that the flow of the turbine increases, the output of the generator also increases, and the entire thermal efficiency is enhanced. Such refuse incinerator systems are disclosed by (1) "Super Refuse-powered Generator System in Steam-jet-type Gas Turbine Method--performance characteristics and examples of their practical study" (Lecture theses published in the 5th Symposium of Power and Energy Technology in 1996, Japan Mechanical Society, 1996-11-13,14); (2) "Performance Characteristics of Refuse-powered Generator System using Steam-jet-type Gas Turbine" (The 8th Symposium of Thermal Technology in Jul. 7, 1995); etc. According to the conventional refuse-powered generator system described above, the output and thermal efficiency of the entire gas turbine increase as the steam-air ratio .alpha. increases (the steam-air ratio a is the ratio of the injected steam Gs to the air intake Ga: namely .alpha.=Gs/Ga). Therefore, when a large volume of residual steam is generated from a refuse incinerator, it is desired that the steam-air specific ratio oz has the largest possible value.
However, in the conventional refuse-powered generator system, there have been the following problems. That is, (1) when the combination of a compressor and a turbine is kept as original, the steam-air ratio .alpha. is approximately 20% to 30% at maximum. A ratio higher than these values disturbs the matching between the compressor and the turbine, and the generator cannot be operated at a constant revolution speed. (2) If the compressor is kept as original and only the turbine is relatively enlarged, the steam-air ratio a can be increased up to, for example about 50% to 60%. If the turbine is made larger, when the operation of a refuse incinerator is stopped, the stable operation of the turbine is not obtained, whereby stable supply of electric power becomes difficult.